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Resonant electron tunnelling assisted by charged domain walls in multiferroic tunnel junctions

Abstract

The peculiar features of domain walls observed in ferroelectrics make them promising active elements for next-generation non-volatile memories, logic gates and energy-harvesting devices. Although extensive research activity has been devoted recently to making full use of this technological potential, concrete realizations of working nanodevices exploiting these functional properties are yet to be demonstrated. Here, we fabricate a multiferroic tunnel junction based on ferromagnetic La0.7Sr0.3MnO3 electrodes separated by an ultrathin ferroelectric BaTiO3 tunnel barrier, where a head-to-head domain wall is constrained. An electron gas stabilized by oxygen vacancies is confined within the domain wall, displaying discrete quantum-well energy levels. These states assist resonant electron tunnelling processes across the barrier, leading to strong quantum oscillations of the electrical conductance.

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Figure 1: Quantum oscillations of the tunnelling conductance.
Figure 2: Cross-sectional scanning transmission electron microscopy images of a La0.7Sr0.3MnO3/BaTiO3 superlattice.
Figure 3: Unit cell mapping of the ferroelectric polarization displacements and the electronic state in the BTO layer.
Figure 4: Electronic structure of the head-to-head domain wall.
Figure 5: Switching of the ferroelectric polarization of the barrier.

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Acknowledgements

Work supported by Spanish MINECO through grants MAT2014-52405-C02-01 and MAT2014-52405-C02-02, MAT2015-066888-C3-1-R, MAT2015-066888-C3-3-R (MINECO/FEDER) and CAM S2013/MIT-2740. The authors thank M. Watanabe for the Digital Micrograph PCA plug-in and A. Lupini for the atomic column mapping scripts. Research at ORNL sponsored by the US Department of Energy (DOE), Basic Energy Sciences (BES), M.V. acknowledges support from Fundación BBVA. G.S. and M.C. acknowledge support from ERC Starting Investigator Grant #239739 STEMOX. J.I.B. acknowledges the Spanish Supercomputing Network (RES) and CeSViMa (project FI-2016-2-0006). J.S. thanks Université Paris Saclay (DÁlembert Program) and CNRS for financing his stay at CNRS Thales.

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J.S. conceived and designed the experiments, discussed and analysed data and wrote the manuscript. J.T. grew the samples and performed transport experiments. D.H.-M., M.C., Z.S. and A.P.-M. helped with growth and transport experiments and discussed results. C.L. discussed and set up experiments, analysed transport data and helped write the manuscript. G.S.-S. and M.V. performed microscopy experiments. S.J.P. and M.V. analysed microscopy data and helped write the manuscript. M.C.M., J.I.B. and D.H.-M. performed and analysed the density-functional theory calculations. M.C.M. helped write the manuscript. C.M., F.M., J.R. and M.G.-H. performed piezoresponse force microscopy experiments. All authors discussed the results and commented on the manuscript.

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Correspondence to Jacobo Santamaria.

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Sanchez-Santolino, G., Tornos, J., Hernandez-Martin, D. et al. Resonant electron tunnelling assisted by charged domain walls in multiferroic tunnel junctions. Nature Nanotech 12, 655–662 (2017). https://doi.org/10.1038/nnano.2017.51

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